1. Field of the Invention
The present invention relates to an apparatus and process for the manufacture of dimensionally accurate die-formed parts.
2. Background Information
U.S. Pat. No. 4,270,890 corresponding to German Patent No. 29 24 704 discloses a device for controlling the height of die-formed parts made from powder material by measuring the distances between the moving die parts and parts or elements fixed to the press frame. In this manner, the thickness of the pressings is measured and compared with the desired size to assume uniformity in dimension of the die formed parts. It is well known in die-forming of parts that the pressures generated create deformation in the press frame, altering the relative distances between the die parts. When the measuring elements are fixed to the press frame, then deformations of the press frame during the pressing will effect the readings produced by the measuring resulting in deviations in the desired height of the die-formed parts. In U.S. Pat. No. 4,270,890, it is disclosed that the measuring elements are fixed in relation to the press and, therefore, are not subject to the effects of any stretching of the press frame produced by high pressing forces.
The more stringent the requirements for precision geometry on a die-formed part, the smaller the tolerances. Consequently, any disruption caused by the elastic deformation of the pressure rams during the pressing process will effect the readings produced by the measuring and accuracy of the die-formed part. For simple die-formed parts (e.g. a cylindrical shape), this effect is insignificant, since the die tools are so rigidly constructed that no significant elastic deformations occur in the range of the pressing force encountered. On more complicated parts with several offsets, as utilized in multi-plate adaptor dies disclosed in German Patent No. 31 42 126 C2, the elastic deformation of the rams can not be ignored. Such die tools have a relatively thin-walled, long and slender shape and not a substantially rigid construction. This type of die tool configuration is subject to significant elastic deformation due to stretching of the press frame, under the action of the pressing force.